From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7A289FA3728 for ; Wed, 16 Oct 2019 22:17:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CD66207FF for ; Wed, 16 Oct 2019 22:17:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571264246; bh=+IG6tGYgGoLbuBZ79yfPKMgVZv30lypkPm307m9NWhE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=OMf/t0sojwz3ofRFNfEoUiVb4MJA0H83Ks8UuVYVm9ZaSZexyjGO99Y/4bN4DzZoa 9zVVMBRaaRhRArLKCOsFLjPaEYNVEYLfioY/OMdDPzjcdwKpAR5VnG+0FVyJgzDccb 557h5t25Mi8R0sQu/1LDbD0n+qnJeL0/wvBSWcBc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732849AbfJPWRY (ORCPT ); Wed, 16 Oct 2019 18:17:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:45098 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2395092AbfJPVyz (ORCPT ); Wed, 16 Oct 2019 17:54:55 -0400 Received: from localhost (unknown [192.55.54.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5B88521928; Wed, 16 Oct 2019 21:54:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571262894; bh=+IG6tGYgGoLbuBZ79yfPKMgVZv30lypkPm307m9NWhE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ozkMzroh/oEI6nE29Lw1ux/fR1QQcdjsGgAMJ2SG1IbRfTS+am/MgqhEEdHq0hb3v CrelDg9DeV2yUvG6aQiIywHmNjm7UR/FwsZ+8BoGLmiB2OcBFJNJsh1NzNJ/Qim/00 jJjGvDV+nvUUdorcyOI6oCKz7vtscCTLZW+fqhgM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Li RongQing , Liang ZhiCheng , Thomas Gleixner Subject: [PATCH 4.9 11/92] timer: Read jiffies once when forwarding base clk Date: Wed, 16 Oct 2019 14:49:44 -0700 Message-Id: <20191016214807.820860828@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191016214759.600329427@linuxfoundation.org> References: <20191016214759.600329427@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Li RongQing commit e430d802d6a3aaf61bd3ed03d9404888a29b9bf9 upstream. The timer delayed for more than 3 seconds warning was triggered during testing. Workqueue: events_unbound sched_tick_remote RIP: 0010:sched_tick_remote+0xee/0x100 ... Call Trace: process_one_work+0x18c/0x3a0 worker_thread+0x30/0x380 kthread+0x113/0x130 ret_from_fork+0x22/0x40 The reason is that the code in collect_expired_timers() uses jiffies unprotected: if (next_event > jiffies) base->clk = jiffies; As the compiler is allowed to reload the value base->clk can advance between the check and the store and in the worst case advance farther than next event. That causes the timer expiry to be delayed until the wheel pointer wraps around. Convert the code to use READ_ONCE() Fixes: 236968383cf5 ("timers: Optimize collect_expired_timers() for NOHZ") Signed-off-by: Li RongQing Signed-off-by: Liang ZhiCheng Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/1568894687-14499-1-git-send-email-lirongqing@baidu.com Signed-off-by: Greg Kroah-Hartman --- kernel/time/timer.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1586,21 +1586,23 @@ void timer_clear_idle(void) static int collect_expired_timers(struct timer_base *base, struct hlist_head *heads) { + unsigned long now = READ_ONCE(jiffies); + /* * NOHZ optimization. After a long idle sleep we need to forward the * base to current jiffies. Avoid a loop by searching the bitfield for * the next expiring timer. */ - if ((long)(jiffies - base->clk) > 2) { + if ((long)(now - base->clk) > 2) { unsigned long next = __next_timer_interrupt(base); /* * If the next timer is ahead of time forward to current * jiffies, otherwise forward to the next expiry time: */ - if (time_after(next, jiffies)) { + if (time_after(next, now)) { /* The call site will increment clock! */ - base->clk = jiffies - 1; + base->clk = now - 1; return 0; } base->clk = next;